| Question |
Answer |
| phosphoglycerides |
composed of glycerol platform esterfied to two fatty acids and a phosphate or phosphate and alcohol |
| what is the simplest phosphoglyceride |
phosphotidate, not a major membrane lipid but is an intermediate in the biosynthesis of other phosphoglycerides |
| Sphingomyelin |
phospholipid that uses sphingosine rather than glycerol as platform, sphingosine is a long hydrophobic amino alcohol. its an N-linked fatty acid and ester-linked phosphorylcholine |
| glycolipids |
have sphingosine platform and N-linked fatty acid, but hydroxyl group is ether-linked to one or more sugars instead of phosphorylcholine |
| how are glycolipids oriented in the cell membrane |
asymmetrically with sugar residues always on the extra cellular side of membrane |
| Cholesterol |
planar molecule, hydrophobic alcohol group interacts with phosphate, rest buried in hydrophobic interior, membrane becomes less prone to phase transition with more cholesterol, bile acid derivatives emulsify fat in SI, steroid hormones derivatives of it |
| Liposomes |
spherical bilayer, as they form they trap in water and any solute present, can be purified away from solvent. used for DNA and drug delivery |
| Integral membrane protein |
interact extensively with the hydrocarbon chains of membrane lipids and can be released only by agents that compete for these nonpolar interactions (detergents). most span the lipid bilayer |
| peripheral protein |
bound to membrane primarily by electrostatic and H-bond interactions with head groups of lipids. can be disrupted by salts and pH change. most bound to surface of integral membrane proteins |
| most common structure of membrane proteins |
Alpha helices |
| how are ion channels made |
Beta sheets form beta barrels, alternate hydrophobic (facing out)membrane side to hydrophilic (facing in)channels side |
| what is unusual about protaglandin H2 synthase |
it is an intergral membrane protein that does not fully span the lipid bilayer |
| structure of Coenzyme A |
ADP core, coupled to pantothenic acid (vitamin B5) which ends in reactive sulfhydryl group. cleavage of thioester bond provide large negative free energy change |
| what catalyzes production of acetyl CoA |
pyruvate dehydrogenase complex |
| what does PDH catalyze |
decabozylation of pyruvate, trasfer of acetyl group to CoA, and capture of two electrons as NADH and H+ |
| prosthetic groups of PDH |
thiamine pyrophosphate (TPP)E1, lipoamide E2 and FAD E3 |
| steps in the conversion of pyruvate into acetyl CoA |
decarbozylation, oxidation, transfer of the resultant acetyl group to CoA |
| PDH step 1 |
ionization of E1-TPP |
| PDH step 2 |
TPP carbanion mounts nucleophillic attack on carbonyl group of pyruvate. loss of CO2 at this step yields hydroxyethyl TPP that can itself form a carbanion |
| PDH step 3 |
Handshake between E1 and E2 allows nucleophilic attack by hydroxyl group carbanion on lipoamide disulfide |
| PDH step 4 |
transfer of acetyl group to CoA by transacetylase site of E2 |
| PDH step 5 |
regeneration of oxidized lioamide by FAD group of E3 subunit (a dehydrogenase) |
| how do enzymes act asymmetrically on symmetric substrates |
three-point landings; if an enzyme binds an achiral molecule at three points, the bound molecule appears to be chiral |
| primary role of NADPH |
anabolic; it provides reducing equivalents required for numerous biosynthetic and detoxification reactions |
| oxidative phase of PPP |
two molecules of NADPH are generated in convering glucose-6-P to ribulose-5-P |
| reaction 1 of PPP |
glucose-6P is oxidized to 6-phosphogluconolactone, NADPH produced. highly exergonic (irreversible) and is the regulatory step of pathway |
| reaction 2 of PPP |
6-phosphogluconolactone is hydrolyzed to 6-phophogluconate by lactonase |
| reaction 3 of PPP |
6-phophogluconate is oxidatively decaroxylated to yield ribulose-5-P. NADPD produced |
| non-oxidative phase of PPP |
A. epimerization and isomerization rxns B. carbon shuffling reactions |
| non oxidative epimerization reaction |
ribulose-5-P epimerase converts ribulose-5-p to xylulose-5-P |
| non oxidative isomerization reaction |
ribulose-5-isomerase converts ribulose5-P to ribose-5-P |
| how many ribulose-5-P are isomerized and epimerized |
2/3 Ru5P produced by oxidative phase are epimerized to X5P. 1/3 isomerized to ribose-5-P |
| Carbon shiffling Rxns |
1. transketolase reaction 2. transaldolase reaction 3. second transketolase reaction |
| transketolase reaction |
transfer of 2 carbon group from xylose-5-P to ribose-5-P. involves cofactor TPP transketolase protein is homologous to phyruvate DH E1 |
| transaldolase reaction |
transfer of 3-carbon group from sedoheptulose-7-P to glyceraldehyde-3-P. does not involve prosthetic group, instead lysine group in active site of enzyme, shiff bases form |
| second tranketolase reaction |
transfer of 2-carbon group from xylulose-5-P to erythrose-5-P. products F6P and G3P both substrates for glycolytic pathway |
| how does chain length and saturation affect melting point.fluidity |
-melting temp increases with chain length -melting temp increases with saturation |
| what is derived from phosphotidate |
the major phosphoglycerides, by the esterification of phosphate group to hydroxyl group of one of the following alcohols, serine, ethanolanmine, choline, glycerol, inositol |
| how do ions and polar molecules cross biological membranes |
protein carriers, channels, and pumps |
| how do membrane lipids diffuse |
freely in two dimensions within their monolayer |
| diffusion of lipids across bilayer (flip flop) |
slow and catalyzed by flopase |
| integral membrane diffusion |
diffuse in two dimensions within the bilayer and never flip flop |
| fluid mosaic bilayer |
bilayers are asymmetric (exterior and interior monolayers differ in lipid composition |
| what modulates fluidity |
cholesterol and fatty acid composition |
| CAC completer cycle overview |
2 carbons enter (acetyl group) and two carbons leave during each cycle (CO2), starting material is regenerated |
| why is O2 needed for CAC |
not needed, but needed to make it go fast, O2 regenerates electron carriers |
| when is energy captured during the CAC |
in coupled reactions, 2 electrons from pyruvate plus 8 electrons and 1 GTP from the cycle |
| where do PDH and CAC reactions occure |
in the matrix of the mitochondria |
| PDH overview |
converts pyruvate (3C) to acetyl group (2C), all catalytic groups returned to original state, |
| Beriberi |
thiamine deficiency, primary symptoms is weakness and neurological problems. endemic to far east food staple rice low in thiamine, also seem in extremely malnourished people, predominately in alcoholics. thiamine administration rapidly reverses |
| mercury toxicity |
mercury and arsenic bind dihydrolipoamide and inhibit PDH. treated by administration of dithiol compounds which competitively inhibit them |
| at what steps can CAC be regulated |
PDH controls flux of carbon, also at isocitrate DH and alpha-KG DH complex |
| how does PDH regulate CAC |
gluconeogenesis requires pyruvate and cannot proceed with smaller chains, hence PDH activity down regulated during gluconeogenesis. once acetyl CoA formed committed to CAC or fatty acid synthesis. cannot be converted to carbs (in animals) |
| glyoxylate cycle |
allows plants and bacteria to make carbs from lipids bypasses 2 carboxylation steps in CAC, succinate used for gluconeogensis. plants contain specialized organelles called glycosomes. animals do not have this pathway |
| metabolic roles of PPP |
1.synthesis of NADPH for reductive biosynthesis 2.synthesis of R5P for nucleotide synthesis 3. when R5P not needed, carbon shuffling rxns convert it to glycolytic intermediates that can be further catabloized |
| where does the PPP take place in eukaryotes |
exclusively in the cytosol |
| what reducing compound is made by PPP |
NADPH |
| pathways requiring NADPH |
SYNTHESIS- fatty acid, cholesterol, nucleotide DETOXIFICATION- reduction of oxidized glutathione and thioredoxin, cytochrome P450 monoxygenases |
| similarities between tansketolase and transaldolase mechanisms |
both forma carbanion intermediate that mounts nucleophic activity on carbonyl carbon. in both cases carbaion is stabilized by resonace and N atom acts as electron sink during cleavage of addition coumpound intermediates |
| primary site of PPP regulation |
the first step, the glucose-6-phosphate rxn. reaction regulated by availability of substrate NADP+. if NADP+ available, G6P will flow into PPP |
| mode 1 of PPP |
cell nedds NADPH and nucleotides (but ATP needs are satified |
| mode 2 of PPP |
cell needs NADPH and ATP (but nucleotide needs are satisfied |
| mode 3 of PPP |
cell needs NADPH and nucleotide and ATP needs are satisfied |
Science Vocab 147928
